Parent-oriented and school-oriented programs that aim to improve child behavior and mental health are well established, few studies focus on the possibility of additional benefits arising from a combined intervention. This study uses a randomized control trial and assesses whether the combination of two standardized evidence-based intervention programs, Triple P (a self-directed parent-oriented intervention that focuses on strengthening parenting skills) and Fit and Strong for Life (a school-based intervention that focuses on stress management skills for children), was more likely to improve parenting and child behavior compared to either program alone and to a no-treatment control group. Data including pre-and post-test measures, as well as four-month follow-up data, were obtained from 78 teachers and 745 parents. Using linear mixed models, results showed that parents in the self-directed Triple P condition engaged in less negative parenting behavior, more positive parenting strategies, scored lower on stress, and reported more parental self-efficacy at post-test. The effects remained at the four-month follow-up. Additionally, after treatment parents in the Triple P condition observed less behavioral problems in their child (although teachers did not). The Fit and Strong for Life intervention yielded no effects in respect to child problem behavior. Last, there was no additional benefit of the combined intervention group above that found for Triple P. This study encourages the utility, practicality, and efficacy of the self-directed Triple P Program and illustrates its effectiveness on positive parenting skills and problem child behavior.